1. Field of the Invention
This invention relates to the field of wheelchairs and other wheeled apparatus for transporting people.
2. Description of the Prior Art
Wheelchairs having a fixed wheelbase width require large main wheels to provide needed stability against overturning. However, the width of such chairs and their wheel size present difficulties in maneuvering the chair in confined spaces such as in washrooms, aircraft, and offices, through doorways, and along narrow aisles.
U.S. Pat. No. 6,164,674 describes a wheelbase adjustable wheelchair. A linkage between two side frames includes two cross members. One end of each being pivotally supported to a side frame on each side of the chair. The cross members are attached mutually at a point of intersection, the other end of each cross member sliding on the opposite side frame.
PCT International Patent Application WO 99/37265 describes a wheelchair having lower and upper side frames, the upper frame being tiltable with respect to the lower frame, ground wheels mounted on the lower frames, and seating and backrest support carried on the upper frames. The upper frame, and the seating and backrest supports are foldable laterally inward regardless of the tilted position of the upper frame.
U.S. Pat. No. 4,603,890 discloses a wheelchair having forward and rearward side frames that are telescopically interconnected so that the length of the frame can be adjusted. A cross brace connecting the side frames permits folding the chair laterally A cross brace mechanism adjusts the width of the chair without adjusting its height.
It is an object of the present invention to provide a wheelchair, the width of whose wheelbase is adjustable. This feature permits the user to readily narrow the chair""s width when narrow doorways and passageways are confronted.
It is another object of the invention to provide a wheelchair having a set of anti-tilting wheels that apply a stabilizing, restoring force to the chair when it is tilted backward. This feature permits safe, reliable backward tilting of the chair by the occupant to avoid or pass-over obstructions at the front caster wheels.
A tilt-in-place wheelchair having adjustable wheelbase includes front and rear side frames, hinged cross members supported on the frames, an adjustment rail supported on the frames for rotation relative to the frames, a block slideably supported on the rail and hinged to one pair of cross members, a latch supported on the rail and adapted for releasable engagement with the rail so that the block is alternately fixed to the rail to maintain the width of the wheelbase or released from the rail to allow adjustment of the wheelbase.
In realizing these objects and advantages a tilt-in-place wheelchair according to the present invention includes a first side frame; a first side frame; a second side frame substantially parallel to the first side frame and spaced laterally therefrom; a first pair of cross members, mutually pivotally interconnected at an inner end thereof and foldable about the pivotal interconnection, a first member of the first pair coupled to and pivotably supported on the first side frame for variable angular positions, a second member of the first pair being coupled to and pivotably supported on the second side frame for variable angular position; a second pair of cross members spaced longitudinally from said first pair of cross members, mutually pivotally interconnected at an inner end thereof and foldable about the pivotal interconnection, a first member of the second pair coupled to and pivotally supported on the first side frame for variable angular position, a second member of the second pair pivotally being coupled to the second side frame for variable angular position; means for adjusting and releasably holding the first pair of cross members and second pair of cross members at predetermined angular positions relative to the first and second side frames; a first tilt wheel extending outward from, and pivotably supported on the first side frame, continually biased resiliently downward toward ground contact and opposing displacement upward away from ground contact; and a second tilt wheel extending outward from, and pivotably supported on the second side frame, continually biased resiliently downward toward ground contact and opposing displacement upward away from ground contact.